1. Field of the Invention
This invention refers to a device for measuring the density of liquids and more specifically to a device for measuring the density of black liquor.
2. Description of the Prior Art
Densimeters of magnetic type are known. As an example of such meters the inventive subject of Swedish Pat. Spec. No. 220,181 may be mentioned, said patent specification illustrating a magnetic densimeter for liquids, wherein a float immersed in the liquid is at its lower end provided with a cylindrical magnet which creates a current in a differential transformer when the float changes its position as the result of a change of density in the liquid. The current from the differential transformer is supplied over an amplifier, a rectifier and a filter to a coil, which in turn attracts the cylindrical magnet so that a new position of equilibrium is achieved in due course.
However, a device of the described type is restricted with regard to its range of measuring, as the device primarily is a laboratory instrument by means of which it is possible to measure the density of liquids of comparatively low viscosity. The measuring must be carried out in a shunted flux, which never provides correct results, as the flux conditions then will have been changed by the shunting.
In certain industrial applications the known devices and methods are not satisfactory, namely for measuring the density of liquids having higher degrees of viscosity, for example black liquor, with the purpose of such measuring being to provide an indication of the content of dry matter in the liquid.
Indeed, densimeters for industrial settings already exist, said densimeters also being capable of being utilized for black liquor in certain cases, but these densimeters have various disadvantages. As examples of this type of densimeter mention may be made of radioactive densimeters, U-tube scales and bubble tubes. The radioactive densimeter may be utilized only for high-viscosity liquor, and furthermore it is in a high price range. Contrary to the radioactive meter, the U-tube scale is solely appropriate for low-viscosity liquor because of the existing danger of contamination and clogging. The bubble tube has substantially the same disadvantages as the U-tube scale.